7.2 Equilibrium Law and Equilibrium Constants

• Two types of equilibria:
  • A homogenous equilibrium has everything present in the same phase.
  • The usual examples include reactions where everything is a gas, or everything is present in the same solution.
  • A heterogenous equilibrium has matter present in more than one phase.
  • The usual examples include reactions involving solids/liquids and gases, solids and solutions.

Equilibrium Law

• The mathematical description of a chemical system at equilibrium.
• aA + bB → cC + dD

Equilibrium Constant, K

• A constant numerical value that defines the equilibrium law for a system.

  

The Haber Process Equilibrium (homogenous system)

• To Calculate the K, plug in concentration values for each entity at equilibrium. Note that K does not have units.

  

Writing an expression for K in a heterogenous system

• Leave out solids and liquids.

K & K’

• K = 1/K’
• K’ = 1/K
• K = [products] / [reactants]
• If K >>> 1 – the reaction is favoured in the forward direction (at equilibrium, there’s a higher concentration of products than reactants
• If K = 1 – the equilibrium overall concentrations of products and reactants are equal
• If K <<< 1 – the reaction is favoured in the reverse direction (at equilibrium, there’s a higher concentration of reactants than products.